Parts made of composite materials are used in a variety of industries, including the aircraft industry. Some hollow composite parts, such as aircraft stringers of a fuselage, are internally supported by a bladder during cure, while externally supported by rigid tool and/or externally compressed via a sealed vacuum bag or other such flexible, impermeable membrane. The bladder typically expands during curing of the composite material into the composite part, and may be susceptible to developing leaks under the high pressure and heat of autoclave curing.
Sometimes leaks are not detected until after the cure cycle has begun. This may occur when smaller undetectable leaks develop into larger detrimental leaks during the added pressure and heat of autoclave cure cycles. Human error may also introduce leaks to the bladders during a stage of the composite manufacturing process in which the bladders cannot be removed or repaired.
During the composite manufacturing process, the composite material may reach a critical cure stage at approximately 190° F.-200° F. If a leak in the vacuum bag or the bladder is discovered prior to this critical stage, the cure cycle can be aborted and the leak can be fixed. For example, an operator can open the door to the autoclave and search for a vacuum bag leak using an ultrasonic microphone. Once the vacuum bag leak is found, it can be repaired. However, since most of the bladder is covered in layers of composite material at this stage, a leak deep within the bladder may be hidden, undetectable, and/or difficult or impossible to fix.